Video processing equipment, in the general sense, is not new. Television studios, for instance, have long been equipped with video editing units which have the capability to take a variety of video source signals and combine the source signals into a single output signal, which is usually a combination or composite of the source signals. Combination of the sources may occur in a variety of ways, ranging in complexity from simple switching from one source to another, as in changing scenes, to complex fades, wipes and dissolves, wherein one source is switched to another by a process of gradual replacement. These units also have the capacity to superimpose one source onto another. This facilitates the placing of titles over scenes and allows one to place an object from one scene onto a background found in another scene, known in the art as chroma-keying.
One such prior art system works in conjunction with an Amiga computer and takes four video inputs, allowing one to switch between the inputs. It does so by simply switching from one input to another, without a dissolve in between (termed an "A/B roller" in the art). As such, it does not allow for mixing or combining the inputs. All of the switching is done to analog signals with analog circuitry (in the analog domain). Following selection of a source by switching, the selected source is digitized to allow capture of a single screen of data from a stream of screens. The system is primarily designed to allow one to extract single frames of video from a source, in particular, to generate animated graphics for recording on video tape. Since it is primarily designed for capturing single screens of data, it is unsuitable for handling multiple streams of video data and is unable to combine such streams into a single output signal dynamically, and therefore fails to meet a need for such capability in the market.
The above-described prior art processes video in the analog domain. Analog processing of video shares the disadvantages found in processing other types of data in an analog fashion.
First is generation loss, whereby successive copies of the video data suffer from degradation due to repeated copying and processing. In other words, each successive copy of the data is worse than the last in terms of resolution and fidelity. In practical terms, one is limited to about three generations before resolution and fidelity become unacceptable. By manipulating the data digitally, the data are only subjected to one generation of loss as data are converted from analog to digital form and back again, thereby allowing an infinite number of manipulations in the digital interim.
Second, it is difficult and costly to store for later use and retrieve video data in analog form. It is far easier to convert the data to digital form and store it, perhaps after it has been subjected to a standard digital data compression algorithm.
Third, it is not possible to compress an analog video signal. Digital data can, therefore, be stored for later retrieval much more efficiently in a compressed form.
Finally, since special analog hardware must be designed for analog video processors such processors are expensive. Digital processors, on the other hand, can be used in conjunction with general purpose computers and can therefore make use of the computer's attendant equipment, thus taking advantage of existing hardware.
The aforementioned prior art is therefore limited to analog processing of data, with all of the attendant disadvantages of such processing. None of the above-described systems is able to combine several different digital video input signals into a single digital video output signal and act thereby as a digital video editor.